Electroceramic devices that exhibit positive thermal coefficients are generally made from doped barium titanate ceramics which have sharp positive temperature coefficients of resistance. Such ceramics are designed so that below a critical temperature, the resistance of the ceramic remains at a low value and is essentially constant. When a particular temperature is reached, a crystalline phase change takes place in the ceramic and this change in the crystal structure is accompanied by a sharp increase in the resistance at the crystalline grain boundaries. The result of this crystalline change is an increase in the device's resistance of several orders of magnitude over a small temperature range. For example, barium titanate heaters with a room temperature resistance of 3.0 ohms can increase to 1,000 ohms or more during a crystalline phase change. The temperature at which crystalline phase change takes place can be adjusted in the manufacturing process through the use of appropriate chemical additives and can attain temperatures as high as 300.degree. C., and even higher.
Commonly, current is carried to the devices by means of lead wires that are attached to metallized coatings which form the electrodes for the electroceramic body. Many ways have been provided for attaching the leads in the past, and this invention especially relates to an improvement in attaching the lead wires to the body.